When Automated Vehicles Cannot Retaliate: Driver-Initiated Takeover Under Aggression in Mixed Traffic

When exposed to aggression from surrounding human-driven vehicles (HDVs), automated vehicles (AVs) with conditional automation adopt defensive responses. However, human drivers may expect to respond with emotion-driven, retaliatory behaviors. This discrepancy between human drivers’ expectations and AV behavior may lead to driver-initiated takeovers, introducing abrupt control transitions and retaliatory driving that threaten traffic safety. In a driving simulator study with 42 licensed drivers, participants experienced different aggressive events (honking, tailgating, and sharp braking) under low and high aggression levels. The results indicated that drivers perceived higher levels of aggression and were more likely to initiate takeovers during sharp braking compared to honking and tailgating, as well as under higher aggression levels. The differences in perceived aggression across event types diminished as the aggression level increased. These findings provide insights into when and why drivers override defensive automation and offer implications for the design of AV behavior in mixed-traffic environments.